A negative glow discharge lamp is comprised of a light-transmitting envelope containing a noble gas and mercury with a phosphor coating on an inner surface of the envelope which is adapted to emit visible light upon absorption of ultraviolet radiation that occurs when the lamp is excited. The lamp is excited by means of the application of a voltage between the lamp electrodes. Current flows between the electrodes after a certain potential is applied to the electrodes, commonly referred to as the breakdown voltage. An elementary explanation of the phenomenon is that the gas between the electrodes becomes ionized at a certain voltage, conducts current, and emits ultraviolet radiation. Examples of typical glow discharge lamps are found in U.S. Pat. No. 2,067,129 to Marden; U.S. Pat. No. 2,403,184 to Lemmers; U.S. Pat. No. 3,814,971 to Bhattacharya; and U.S. Pat. No. 4,408,141 to Byszewski et al.
Reference is also made herein to U.S. Pat. No. 4,904,900 which issued to Bouchard et al on Feb. 27, 1990 and is assigned to the same Assignee as the present application. The Bouchard et al patent teaches a negative glow discharge lamp that includes a light-transmitting envelope containing a noble gas fill material and a pair of electrodes disposed in the envelope. The anode electrode is comprised of a refractory metal piece, such as a molybdenum foil strip, supported from one end of a single lead-in wire that is preferably swagged to the metal strip.
Although the above-described negative glow discharge lamp of Bouchard et al has been employed with a high degree of success, it has been found that certain disadvantages do exist. More specifically, it has been found that if an insufficient pressure is applied to the end of the lead-in wire, the molybdenum foil may separate from the swagged lead-in wire during lamp operation leaving the remaining lead-in wire to function as the anode electrode. We have discovered that the reduced surface area of the remaining anode wire may run excessively hot during operation and greatly diminish the light output due to evaporation of the anode wire end. Additionally, the swagging operation adds cost and complexity to the lamp.